Method of recovering alumina from silicates



July 18, 1933- F. M. MCCLENAHAN METHOD OF RECOVEING ALUMIN FROM SILICATES Filed oct. 51, 1929 kmm ENRE EG Patented .lilly 18, 1933 narran stas MTHD OF RECOVERING AL'UMIIA '53.0141 SILIGATES Application filed October` 31, 1929. Serial No. ZV03,917.

' which materials used to treat the aluminum or fluoride compounds may be recovered and re-used for treating successive batches. Other objects and advantages Will appear as the specification proceeds.

In my United States Patent No. 1,426,890 I have described a method of treating silicates,

in which the silicates are digested in an aqueous solution of the biiluoride of ammonium, the precipitate being separated from the ltrate. In this method the lltrate Was made alkaline by the addition to it of ammo-nium hydrate, and the resulting ammonium uoride Was separated from the insoluble silicic acid.

In my United States Patent No. 1,426,891 I have described the formation oi' the compound AlFgNI-LF as the typical aluminous product of the digestion of an aluminous silicate with the biliuoride ot ammonium. The tenacity of the union oi these tivo uorides was pointed out, and a method was proposed for their treatment.

rIhe accompanying drawing is a flow sheet of the process involved.

In this application, it is proposed to treat such an aluminum-ammonium double iuoride, which was described as atypical alu-v minous product of the digestion of an aluminous silicate with the billuoride of ammonium, to produce the oxide otaluminum.

of the volatilized ammonium'luoride transamounts if the silicate digested With the ammonium biduoride Were eldspars; but, if the original silicate is kaolin or related mineral not lcontaining potassium or sodium or other metals in large amount, the material may be considered more or less purely a silicate of aluminum, and all other components may be considered as impurities. The naturally occurring impurities (metallic) in kaolin are principally iron and titanium.` One 50. of the purposes of the invention is to provide methods of disposing of these two naturally occurring impurities so as to produce commercially pure oxide of aluminum.

The digestion of a silicate With the bluoride oi ammonium produces tvvo divisions of products, namely the Water-solubles, and the Water-insolubles. In a copending application, Serial No. 393,122, I have dealt With the principal Water-soluble. The outstanding Water-insoluble of such digestion of lraolin, or lraolin-related. silicates, is the double fluoride or fluorides of ammonium and aluminum, and it is this insoluble Which furnishes the starting material for my process, hereinafter described.

' lNhen the Water-solubles are iiltered from the Water-insolubles, it is difiicult to free the latter completely from the former, and it is not economic to endeavor to do so completely with Water Washing. Nor is it economic to drive oil the volatilizable materials from the non-volatilizables by use or' heat, until the great bulk of the Water-solubles have been separated from the Water-insolubles by Washing. When, however, this Washing shall have been taken to the economic limit, there remains behind a sludge comprising principally aluminum fluoride associated as a double component With ammonium fluoride. Incidentally there will be more or less contamination with titanium and iron fluorides in double salt union with ammonium liuoride. The calcining of this Washed sludge drives oli" rst the ammonium Silico-fluoride; then the double iiuoride ot iron 'and ammonium is broken up, the latter going over vas a vaporized material and, finally, the streaming forms the ammonium titano-tluoride to titanium nitride (typical :-Ti3N4). A pro- Visional chemical equation may be taken as the following the silica, and all ot the ammonia will have been driven from the system by the calcining at a temperature approximating 400 C.

The vapors emanating from the calcining equipment are prevailingly NH4?? with notable amounts fof (NHQgSiFG and NHiF-TF.. The color of the residue becomes bull to salmon, and the appearance of this color indicates substaiitiallythe end-point of the calcining so far .as silicon and .ammonium compounds are concerned in the outgoing stream of vapors. l

The residue comprises chielly AlFS, 'and FeF2 or FeF8 in a small amount, and Tial .i in a small .amo-unt For the purpose of simplication, l shall call this residue"ineal. The next step propose for this material is to subject it to a progressive treatment from digestion, through drying, to calcining at approximately 400 C. with ammonium sulfate and sulfuric acid, in the proper proportions, to bring about the reactions provisionally explained by the following chemical equation:

Since the aluniinous composition of the meal7 by far exceeds the titanium content the HF evolved will be relatively very large with respect to the titaiiiuni'nitride present. For instance the molecular ratio of aluminum to titanium may easily be vas muchas iitteen times the titanium. In thisl case, I would suggest that we might expect approximately as many as ninety molecules of HF for each atom of Ti.

By increasing the mass of the HF in the reaction on the nitride Without an accoinpanying stream of Nl-LF the equation noted above, in which the nitride itselt` is explained, becomes reversed, and the nitride is re-transformed to the ammonium titano-fluoride. The provisional equation explanation is given at this place:

risueoiirmm)grirseerirniiir.

All of these products in the right hand term of the equation aie volatile under the conditions of the treatment.

Therefore, early in the reaction of the mixed sulfates on the meal the titanium is carried out of the'system as is also the iluor'- ine. This reaction is completed when the evolution of luorine, derived from the alumi num fluoride, is completed. The evolution is completed When the aluminum is changed to a more or less dehydrated ammonium alum.

rThe next step is the raising of the mass to approximately 4h00o C., whereby the ollovving reaction takes place (NH4) SOM-A1203 -i- SHgSOi ing. However, the streaming of ammonium sulfate from this compound is accompanied by la hydrolizing of the aluminum sulfato to alumina Aand sulfuric acid. The ammonium sulfate, upon volatilization, has an endo@ thermic etlect, by Which the alumina is inhibited from crystallizing. The ,so-called Water of crystallizationis. in tact Water ot constitution and acts as a chemical re-'agent upon the aluminumvsulfate in the hydrolizing action described.

The volatiliaed 'ammonium and hydrogen sulfates are in the same proportion as used in the digestion-of the meal. and maybe re- 'turned'ivithout loss to anew batch ot meal.

The temperatures of the evolution of' the HF with its titanium content and this liinal production'of alumina are Widely separated, which allows 'the .first volat-ilized products to 'be trapped one Way and returned as bifluoride of ammonium in the digest-ion'of a fresh batch of liaolin. The trapping of the products volatilized at a higher temperature allows them to be preserved'in high etli'ciency and re-used as described.

The hot calcined residue may be puriiied and treed from contamination With iron oxide by .salting it With ammonium chloride and continuingr the calcining. By this method, the iron chlorides are volatilized and may be trapped along with the excess of ammonia. The resultant product is an alumina of very high purity and which is readily soluble iii both alkali-es andl acids. By Well-known methods the alumina, or oxide of aluminum,

. may be reduced to the metal aluminum.

While in the foregoing description I have stated particular ree-agents and treating niaterials, it will be understood that other equivalent re-agents or materials may befused Without departingfrom the spirit of my invention. Also, it is obvious that other steps may be substituted for the steps in the processes or methods outlined, Which are Well-known chemical equivalents for accomplishing the same results. 1

The foregoing detailed description has been given by Way of example and for cle`arness of understanding-only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible, in vieu of the prior art.

lVhat l regard as new, and desire to claim by Letters Patent, is:

l. ln a process forV the production of alumina, comprising preparatorily digestingl an aluminous silicate with a fluoride of ammonium to obtain a residue containing aluminum ammonium fluoride, heating said residue, and treating the residue to remove impurities, said last mentioned treatment comprising digesting the residue with ammonium sulfate and heating the mass.

2. ln a process for the production of alumina, the steps comprising decomposing the ammonium-aluminum iiuorides derived from said silicates through heating said iiuorides at atemperature suilicient to volatilize the dissociated ammonium iiuoride compounds, digesting the mass With sulfuric acid, ammonium sulfate, and Water and heating to remove the volatile products.

3. In a process for the production of alumina, the steps comprising decomposing the ammonium-aluminum fiuorides derived from said silicates through heating` said fluorides atatemperature suflicient to volatilize the dissociated ammonium uoride compounds, digesting the mass with sulfuric acid, ammonium sulfate, Water, heating to remove the volatile iiuorine products of said digestion, and recovering said products.

el. ln aI process for the production of alumina, the steps comprising decomposing the ammonium aluminum fluorides derived from said silicates through heating said iiuorides atatemperature suliicient to volatilize the dissociated ammonium fluoride compounds, digesting the mass with sulfuric acid, ammonium sulfate and Water heating to remove the volatile fluorine products of said digestion, and re-using said volatile products in treating a new batch of silicates. 4 5. ln a process for the production of alumina, the steps comprising decomposing the ammonium-aluminum fluorides derived from said silicates through heating said fluorid-es at a temperature suflicient to volatilize the dissociated ammonium fluoride compounds, digesting the mass With sulfuric acid, ammonium sulfate, Water, and raising the temperature of the residue to a suiiicient degree to decompose the sulfates.

6. In a process for the production of alumina, the steps comprising decomposing ammonium-aluminum fluorid'es from said silicates through the agency of heat at a temperature sufcient to volatilize the dissociated ammonium-fluoride compounds and carry the volatilized products from the presence of the non-volatile aluminum fluoride, digesting the mass with acid ammonium sulfate, and

to obtain the ammonium-aluminum fluorides,

heating the mass until the residue assumes a color which is substanti lly buff to salmon,

digesting the residueivith acid-ammonium sr ate to remove the. fluorine compounds, and calcininO the residual mass. l

8. ln a process for the production of alumina, the steps comprising preparatorily die gesting silicatesiv'th a fluoride of ammonium to obtain ammonium-aluminum fluorides, heating the material until the residue assumes a color which is substantially bur1 to salmon, digesting the residue with acid-,1 90

ammonium sulfate, heating the mass to vola tilize the titanium present, and calciningthe residues.

l9.y lne process for the production of alumina, the steps comprising preparatorily digesting an aluminum silicate with a fluoride of ammonium to obtain a residue containing aluminum-ammonium fluoride, heating the mass to obtain a non-volatile residue, di-

gesting the residue with aluminum sulfate and sulfuric acid, evaporating the mixture to dr? ness, and calcining the mass vto obtain a volatile acidammonium sulfateV product and a non-volatile alumina product.

l0. in a process for the production of alumina, the steps comprising preparatorily di,n gesting an aluminous silicate With a iiuoride of ammonium to obtain a residue containing aluminum-ammonium iiuoride, heating the mass to obtain a non-volatile residue, digesting the residue with ammonium sulfate and sulfuric acid and heating the mass in the presence of ammonium chloride. p

l1. ln a process for the production of alumina, the steps comprising preparatorily digestinfc,` an aluminous silicate Wit-h a fluoride of ammonium to obtain a residue containing aluminum-ammonia luoride, digesting the residue with ammonium sulfate, sulfuric acid and Water, evaporating the mixture to dry mass to obtain a non-volatile residue, digestying the Imass with aeiclemmonum .sulfate, `and ealeiniug' the residue". ,I

13. In a `process for'tlieprod'uction 4ofalumina, the `steps comprising `prepaatorly digesting en aluminous Vwsilicate With ialiuorde `of ammcuium to obtain a residueeontaining aluminumammonium fluoride, heating the massvtodryness, digestingfthe residue With ammonium sulfate and sulfuric acid, and calciuing the mass. Y Y' 14. u a process for 'the production of alumina, the steps comprising' preparatorily digesting aluminous silicates in the presence of a fluoride of ammonium to produce a sludge containing ammonia-aluminum fluo'rides and other metallic fluorides, decomposing' the sludge loy heating at a temperature sufcieutly elevated to :dissoeiatevsaid I muterialsluto volatile,and/nonvolatile fracf "vapor-ating.thefiltrate toclryness, oaloining the dryfurassfreccvering the 'volatile product of acid-ammonium sulatevevolvedin the calciniugoperation,.and calci-ning.;` the monvolatile alumina in the presencefof-ammonium 'chloride to .remove .the iron.

FRNCS MITCHELL: MCCLENAHAN.

VVA 

